IPC is an absolute must. Good for three days but its possible to stretch it to a week if you really want to slow down (it's not a stereotyped "tropical paradise" though).
Entry to Chile at SCL will cause you to pay Immigration (US $ Cash) somewhere between $30 and $50 or more - depending on the words on the cover of your passport. The only way to avoid it is to have a Chile stamp already in your passport. It's not covered in the tax component of your ticket. Be warned!